An RAF officer examines the impact point of a 'Grand Slam' 22,000 lb bomb dropped on the U-boat factory at Farge, near Bremen, on 27 March 1945. The site at Farge – codenamed Valentin - was one of several hardened U-boat assembly facilities planned by the Germans in response to Allied bombing. Protected by massively thick roofs of reinforced concrete, they were invulnerable to all conventional bombing. Construction work was almost complete when 617 Squadron attacked on 27 March 1945. Of 12 'Grand Slams' dropped, two penetrated the 15 ft ferrous concrete roof and exploded, collapsing much of the structure.

Grand Slam bomb impact

RAF bombs from the biggest,Grand Slam 22,000 lbs,Tall Boy 12,000 lbs to the smallest 40 lbs GP.

RAF bombs

A Lancaster B Mark I (Special) of 617 Squadron releases its 22,000 lb 'Grand Slam' deep penetration bomb over the Arnsberg viaduct in Germany, 19 March 1945. Arnsberg lay in the eastern Ruhr Valley, not far from the Mohne dam, which had been the target for 617’s first operation in 1943. Now, its strategically important railway viaduct was the objective. On 19 March 1945 an attack by 19 Lancasters of 617 Squadron carrying a mixture of 'Tallboy' and 'Grand Slam' bombs brought it crashing down.